Ni-Enhanced Charge Transport via π-π Stacking Corridor in Metallic DNA

The mechanism underlying DNA charge transport is intriguing. However, poor conductivity of DNA makes it difficult to detect DNA charge transport. Metallic DNA (M-DNA) has better conducting properties than native DNA. Ni²⁺ may chelate in DNA and thus enhance DNA conductivity. On the basis of this finding, it is possible to reveal the mechanisms underlying DNA charge transport. The conductivity of various Ni-DNA species such as single-stranded, full complement, or mismatched sequence molecules was systematically tested with ultraviolet absorption and electrical or chemical methods. The results showed that the conductivity of single-stranded Ni-DNA (Ni-ssDNA) was similar to that of a native DNA duplex. Moreover, the resistance of Ni-DNA with a single basepair mismatch was significantly higher than that of fully complementary Ni-DNA duplexes. The resistance also increased exponentially as the number of mismatched basepairs increased linearly after the tunneling current behavior predicted by the Simmons model. In conclusion, the charges in Ni²⁺-doped DNA are transported through the Ni²⁺-mediated π−π stacking corridor. Furthermore, Ni-DNA acts as a conducting wire and exhibits a tunneling barrier when basepair mismatches occur. This property may be useful in detecting single basepair mismatches.     

Carbazole and arylamine functionalized iridium complexes for efficient electro-phosphorescent light-emitting diodes

We report the synthesis and characterization of four cyclometalated iridium complexes based on carbazole and arylamine modified 2-phenylpyridine. The carbazole and arylamine groups are linked to 2-phenyl pyridine backbone to enhance the energy harvesting and transfer from host to guest materials. The electrochemical and photophysical properties of the complexes are studied and electroluminescent devices are fabricated. The results show that the complexes with ligands containing carbazole moieties have desirable phosphorescent properties. The device with complex 3 doped PVK (poly (vinylcarbazole)) as emission layer achieves maximum luminous efficiency of 6.56 cd A⁻¹ and maximum brightness of 14448 cd m⁻².     

Four new copper(II) complexes with di-substituted s-triazine-based ligands

In this paper, two di-substituted triazine-based ligands, 6-chloro-N,N,N′N′-tetrakis-pyridin-2-ylmethyl-[1,3,5]triazine-2,4-diamine (L1), and 6-chloro-N,N′-bis-pyridin-2-ylmethyl-N,N′-bis-thiophen-2-ylmethyl-[1,3,5]triazine-2,4-diamine (L2), have been prepared. Reaction of CuCl₂·2H₂O and Cu(NO₃)₂·3H₂O with L1 and L2 results in the formation of [Cu₂Cl₄(L1)]·3MeOH (compound 1), [Cu₄(NO₃)₈(L1)₂]·2.07CH₂Cl₂·0.93MeOH (compound 2), [Cu₂Cl₄(L2)₂] (compound 3) and [Cu(NO₃)₂(L2)]·CH₂Cl₂ (compound 4), respectively, which have been fully characterized and determined by single-crystal X-ray crystallography, FT-IR, elemental analysis, thermogravimetric measurement and magnetic susceptibility. The dinuclear compound 1 shows strong π-π interactions between the neighboring pyridine rings. The nitrate-π (1,3,5-triazine ring) interaction with the distance of 2.755 Å in compound 2, is the closest contact reported so far. Compounds 3 and 4 are mononuclear copper(II) compounds, in which none of thiophene rings coordinates with copper(II) ion. In addition, the different orientations of two thiophene rings in compounds 3 and 4 lead to the π-π and CH₂Cl₂-π (thiophene ring) interactions in compound 4, but not in compound 3.     

Synthesis and structure of a lead(II)-citrate: {Na(H2O)3}[Pb5(C6H5O7)3(C6H6O7)(H2O)3]·9.5H2O

The reaction of lead(II) nitrate with trisodium citrate Na₃(C₆H₅O₇) in a 1:22.5 ratio at pH 4.8 provides crystals of {Na(H₂O)₃}[Pb₅(H₂O)₃(C₆H₅O₇)₃(C₆H₆O₇)]·9.5H₂O (1). The structure of 1 is two-dimensional and exhibits five distinct Pb(II) sites and four different modes of citrate bonding. The five lead sites all display hemidirected coordination geometries, that is, irregular distribution of neighboring oxygen atoms resulting in obvious gaps in the coordination spheres. Consequently, the lead coordination geometries exhibit proximal bonding to a number of oxygen donors, as well as distal interactions with nearest neighbors. The coordination numbers vary from 8 to 10, with ‘5+3’, ‘5+4’, ‘6+4’ and ‘7+3’ coordination modes where the first number refers to the proximal ligands and the second to the distal set. The four crystallographically distinct citrate groups include three with deprotonated carboxylate groups (C₆H₅O₇)³⁻ and one with a single protonated carboxyl group (C₆H₆O₇)². The citrate ligands bridge 3, 5, 7 and 7 lead sites. Three of the citrate groups exhibit tridentate chelation coordination to a lead site through two carboxylate oxygen donors and the hydroxyl groups. One citrate group projects an uncoordinated -OH group and a pendant protonated carboxyl group into the interlamellar domain. This latter carboxyl group coordinates to a sodium cation, which exhibits five coordinate geometry defined by three aqua ligands and the carbonyl oxygen of the -CO₂H groups in the basal plane and a citrate -OH donor in the apical position.     

Genome sequence of the 17β-estradiol-utilizing bacterium Sphingomonas strain KC8

Sphingomonas strain KC8 is known for its ability to utilize 17β-estradiol, a natural estrogen and an environmental endocrine-disrupting compound, as the sole carbon and energy source. Here, we report the draft genome sequence of the strain KC8 (4,074,265 bp, with a GC content of 63.7%) and major findings from its annotation.     

Quantitative mass spectrometry reveals the epigenome as a target of arsenic

Recent studies reveal that posttranslational modifications on chromatin proteins, especially histones, organize genomic DNA and mediate various cellular responses to environmental influences. Quantitative mass spectrometric analysis is a powerful approach to reveal these dynamic events on chromatin in a systematic manner. Here, the effects of arsenic exposure on histone epigenetic state were investigated in human UROtsa cells, and a reduction in acetylation level on several histone H3 and H4 lysine residues was detected. Furthermore, MYST1 was shown to be the major histone acetyltransferase for H4 Lys16 and protect UROtsa cells from arsenic toxicity.     

Expression of an Oncidium gene encoding a patatin-like protein delays flowering in Arabidopsis by reducing gibberellin synthesis

The involvement of lipase in flowering is seldom studied, and this research provides evidence that fatty acids produced by lipase affect flowering. OSAG78 encoding a patatin-like protein was isolated from Oncidium Gower Ramsey. OSAG78 fused with green fluorescent protein was found to localize at the cell membrane. Transgenic Arabidopsis overexpressing OSAG78 demonstrated higher lipase activity than the wild-type control. In addition, the amount of free linoleic acid and linolenic acid in transgenic Arabidopsis was found to be higher than that in the wild type. Transgenics overexpressing OSAG78 exhibited altered phenotypes, including smaller leaves and rounder flowers, and also demonstrated a late flowering phenotype that could be rescued by gibberellin A(3) (GA(3)) application. Several flowering-related genes were analyzed, indicating that the expression of gibberellin-stimulated genes was decreased in the plants overexpressing OSAG78. Also, the expression of AtGA2ox1, AtGA3ox1 and AtGA20ox1 genes encoding GA2-, GA3- and GA20-oxidases, respectively, which are mainly responsible for gibberellin metabolism, was decreased, and the level of GA(4), a bioactive gibberellin, measured by gas chromatography-mass spectrometry was also reduced in the overexpressing lines. Furthermore, the expression levels of AtGA3ox1 and AtGA20ox1 were significantly decreased in wild-type Arabidopsis treated with linoleic acid, linolenic acid or methyl jasmonate. The membrane-bound OSAG78 might hydrolyze phospholipids to release linoleic acid and linolenic acid, and then depress the expression of genes encoding GA3- and GA20-oxidase. These changes reduced the bioactive gibberellin level, and, finally, late flowering occurred. Our results indicate that a patatin-like membrane protein with lipase activity affects flowering through the regulation of gibberellin metabolism.     

Crystal structure of tarocystatin–papain complex: implications for the inhibition property of group-2 phytocystatins

Tarocystatin (CeCPI) from taro (Colocasia esculenta cv. Kaohsiung no. 1), a group-2 phytocystatin, shares a conserved N-terminal cystatin domain (NtD) with other phytocystatins but contains a C-terminal cystatin-like extension (CtE). The structure of the tarocystatin–papain complex and the domain interaction between NtD and CtE in tarocystatin have not been determined. We resolved the crystal structure of the phytocystatin–papain complex at resolution 2.03 Å. Surprisingly, the structure of the NtD–papain complex in a stoichiometry of 1:1 could be built, with no CtE observed. Only two remnant residues of CtE could be built in the structure of the CtE–papain complex. Therefore, CtE is easily digested by papain. To further characterize the interaction between NtD and CtE, three segments of tarocystatin, including the full-length (FL), NtD and CtE, were used to analyze the domain–domain interaction and the inhibition ability. The results from glutaraldehyde cross-linking and yeast two-hybrid assay indicated the existence of an intrinsic flexibility in the region linking NtD and CtE for most tarocystatin molecules. In the inhibition activity assay, the glutathione-S-transferase (GST)-fused FL showed the highest inhibition ability without residual peptidase activity, and GST-NtD and FL showed almost the same inhibition ability, which was higher than with NtD alone. On the basis of the structures, the linker flexibility and inhibition activity of tarocystatins, we propose that the overhangs from the cystatin domain may enhance the inhibition ability of the cystatin domain against papain.